Mejda Abassi

Responses of leaf growth and gas exchanges to salt stress during reproductive stage in wild wheat relative Aegilops geniculata Roth. and wheat (Triticum durum Desf.)

In order to investigate the effect of salinity on the growth and photosynthesis of the wild wheat and wheat, three accessions of Aegilops geniculata from Ain Zana, Zaghouan and Sbitla and one variety of durum wheat (Triticum durum) were grown in the INRAT greenhouse and treated with different salinity levels. The growth of leaves, water status and gas exchange parameters have been measured at the reproductive stage. The flag leaf length, total leaf dry weight, water status, CO2 assimilation rate, stomatal conductance, intercellular CO2 and transpiration for the three Ae. geniculata accessions and wheat variety significantly decreased with increasing salt. The decline in photosynthesis measured in response to salt stress was proportionally greater than the declines in transpiration, resulting in a reduction of water-use efficiency, at both the leaf and whole-plant levels. Among the factors inhibiting photosynthetic activity, those of a stomatal nature had a greater effect. This study has shown a high degree of variation of these characters mainly related to geographical origin. It was observed also that Sbitla accession was less affected by the imposed salt stress than all the others while Ain Zana was the most affected one.

Morphogenetic responses of Populus alba L. under salt stress

The morphogenetic responses to salt stress of Tunisian Populus alba clones were studied in order to promote their plantation in damaged saline areas. One year-old plants of three P. alba clones (MA-104, MA-195 and OG) were subjected to progressive salt stress by irrigation during two consecutive years. The plants were grown in a nursery, inside plastic receptacles containing sandy soil and were irrigated with tap water (control) or 3–6 g/l NaCl solution. During this study, leaf epinasty, elongation rate, vigor, internode length, plant architecture, and number of buds were evaluated. Test clone response was highly dependent on the applied treatment and degree of accommodation. The most pronounced alterations were induced under 6g/l of NaCl treatment including leaf epinasty, leaf elongation rate delay, vigor decrease, internode length shortening, and morphogenetic modifications. These responses were less noticeable in the MA-104 clone with respect to the two other clones. The salt effect induced a delay in the leaf elongation rate on the MA-195 and OG clones leading to an early leaf maturity. The vigour and internode length of the MA-104 clone was less affected than the other clones. The OG clone was the most salt-sensitive thus, it developed shorter branches and more buds number than MA-195 and MA-104. The effect of long-term salt stress was to induce early flowering of the P. alba clones which suggests that mechanism of salt accommodation could be developed.

Adaptations micromorphologiques foliaires développées par le peuplier blanc (Populus alba L.) face à la salinité

Résumé L’étude de l’effet du NaCl a été suivie sur trois clones de peuplier blanc (MA-104, MA-195 et O.Gherib). Certains paramètres micromorphologiques foliaires ont été mesurés. Les résultats suggèrent que les différences inter et intraspécifiques relevées sont principalement liées à la diversité des conditions écogéographiques des lieux d’origine. En effet, le clone MA-104 a développé la plus forte densité de trichomes et de stomates. Il a montré une plasticité des stomates mise en évidence par une réduction de la longueur et de l’ouverture des ostioles. Le clone MA-195 a montré une moindre augmentation du nombre de stomates par comparaison à MA-104, mais l’ouverture de ses ostioles a été réduite. Le clone O.Gherib a révélé la plus faible densité stomatique et l’absence de réduction de l’ouverture des ostioles correspondant à une faible tolérance à la salinité.

Allelopathic effects of leachates of Casuarina glauca Sieb. ex Spreng. and Populus nigra L. on germination and seedling growth of Triticum durum Desf. under laboratory conditions

The decline in soil fertility and the poor distribution of precipitation during the growth and maturation of cereal crops are major constraints to improving yields in the Mediterranean zone in North Africa. The use of agroforestry species is one strategy for enhancing agronomic productivity and supporting a range of ecosystem services and environmental benefits. However, to our knowledge, the allelopathic effects of these agroforestry species on cereals are poorly documented under Mediterranean conditions. The effects of three aqueous extracts (leaves, roots and litter) from two agroforestry species (Casuarina glauca Sieb. Ex Spreng. and Populus nigra L.) have been evaluated for their allelopathic potential on seed germination and seedling growth of Triticum durum Desf. under laboratory conditions. These allelopathic effects were evaluated using several parameters including seed germination, total dry mass, root and shoot length, chlorophyll and protein concentrations in T. durum seedlings along with phenolic compounds in different parts (leaves, roots and litter) of the two allelopathic species. Exposure to the different extracts of C. glauca and P. nigra significantly reduced germination kinetics, dry mass production, root and shoot length, and chlorophyll and protein concentrations in T. durum seedlings. This reduction was significantly more pronounced for the different extracts from P. nigra. Our results showed a significant negative correlation between dry mass accumulation in T. durum seedling and polyphenol concentration. Overall, the findings of the present study support the introduction of C. glauca into the agroforestry system. However, field monitoring under natural conditions would be necessary to confirm in practice the results obtained with the bioassays.